Currently, many tools are equipped with strain gauges for measuring the twisting forces applied to the tool. Thereby the user can view the value of the strain gauge to decide the force applied to the tool. Thus the screw can be driven properly without breakage.
In the prior art, strain gauge spanner has the function of the measuring twisting force, but the driving end of the spanner has a fixed type. The diving end is not replaceable. Thereby when users desire to drive screws of different sizes, the user must buy another spanner with the strain gauge. One spanner has respective strain gauges. This induces a high cost. Furthermore, it is often that the user has no desire to buy a strain gauge tool due the finite use thereof. Only the old form spanners are used.
Furthermore, the orientation of the driving end of the spanner with respect to the handle of the spanner is always in a fixed angle. Thereby in some places not suitable for the orientation of the driving end, the user will feel uneasy in operation.